Assessment of the Efficacy, Safety, and Tolerability of AVP-786 (Deudextromethorphan Hydrobromide [d6-DM]/Quinidine Sulfate [Q]) for the Treatment of Agitation in Patients With Dementia of the Alzheimer's Type

Inclusion Criteria: * Diagnosis of probable Alzheimer's Disease (AD) according to the 2011 National Institute on Aging-Alzheimer's Association (NIA-AA) working groups criteria * Participants with clinically significant, moderate/severe agitation at the time of screening and for at least 2 weeks prior to baseline that interferes with their daily routine and for which a prescription medication has been indicated, in the opinion of the investigator * The diagnosis of agitation must meet the provisional consensus definition of agitation in participants with cognitive disorders developed by the International Psychogeriatric Association (IPA) Agitation Definition Work Group. * A Clinical Global Impression of Severity of Illness scale for Agitation (CGIS-Agitation) score of ≥ 4 (moderately ill) at screening and baseline * Participants must have a reliable caregiver who is able and willing to comply with study procedures, including not administering any prohibited medications during the course of the study. * Caregiver who is able and willing to comply with all required study procedures. In order to qualify as a reliable informant (i.e., caregiver) capable of assessing changes in participant's condition during the study, the individual must spend a minimum of 2 hours per day for 4 days per week with the participant. Exclusion Criteria: * Participants with dementia predominantly of the non-Alzheimer's type (e.g., vascular dementia, frontotemporal dementia, Parkinson's disease, substance-induced dementia) * Participants with symptoms of agitation that are not secondary to AD (e.g., secondary to pain, other psychiatric disorder, or delirium) * Participants with co-existent clinically significant or unstable systemic diseases that could confound the interpretation of the safety results of the study (e.g., malignancy, poorly controlled diabetes, poorly controlled hypertension, unstable pulmonary, renal or hepatic disease, unstable ischemic cardiac disease, dilated cardiomyopathy, or unstable valvular heart disease) * Participants with myasthenia gravis